The total quantity and concentration of six herbicides, isopropyl m-chlorocarbanilate (chlorpropham), 2-chloro-4-(ethylamino)-6-(isopropylamino-s-triazine (atrazine), 3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea (linuron), 2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide (alachlor), 3-amino-2,5-dichlorobenzoic acid (chloramben), and (2,4-dichlorophenoxy)acetic acid (2,4-D), in unaerated, aqueous solutions absorbed by seeds of 11 soybean (Glycine max (L.) Merr.) strains were measured. Mechanism of movement of the herbicides from the aqueous solutions to the seeds in the experimental procedure employed was diffusion. Total quantity and concentration of herbicide found in the seeds differed significantly for both herbicides and soybean strains. Total quantity of herbicide absorbed was determined by total oil and percent oil of the seeds. The capacity of the seeds to absorb a given herbicide was more closely related to percent oil of the seeds than to total oil of the seeds. The emergence and seedling shoot weight of ‘Cutler’ soybeans were not affected appreciably by concentrations of linuron, atrazine, and chloramben (potassium salt) but were reduced by high concentrations of chlorpropham and alachlor and relatively low concentrations of 2,4-D (potassium salt) in the seeds.

The effect of 1.0 ppmw fluridone {1-methyl-3-phenyl-5-[3-trifluoromethyl)phenyl]-4(1H)-pyridinone} on growth of American pondweed (Potamogeton nodosus Poir.) and sago pondweed (Potamogeton pectinatus L.) was examined in plants kept in darkness or under various numbers of 12-h photoperiods. When plants were exposed to 1.0 ppmw fluridone for 1 to 10 12-h days, no stunting of American pondweed occurred until 21 days after treatment. Thirtythree days after treatment, plants that had received 4 to 10 days' exposure were most stunted. Sago pondweed was slightly more susceptible than American pondweed (87% and 50% reduction in length, respectively) 37 days after a 10-day exposure. Chlorophylls a and b were significantly lower in both species 14 days after all fluridone treatments. American pondweed plants exposed to fluridone continuously (1.0 ppmw) for 15 days, but given 0, 3, 6, 9, 12, or 15 12-h days were stunted only after having received at least six photoperiods. Stunting in sago pondweed was only slightly light-dependent. Neither species absorbed significantly more 14C-labeled fluridone after 2, 4, or 14 photoperiods compared to plants kept in darkness for the same time.

Interactions between carbamate and growth regulator herbicides were antagonistic both in whole plants and in plant segments. When combinations of isopropyl m-chlorocarbanilate (chlorpropham) and (2,4-dichlorophenoxy)acetic acid (2,4-D) were applied to the foliage of either redroot pigweed (Amaranthus retroflexus L.) or pale smartweed (Polygonum lapathifolium L.), the severe twisting effects of 2,4-D were greatly reduced. This interaction did not involve differential movement or metabolism of either herbicide. The induced elongation of soybean hypocotyl sections by the three growth regulators 2,4-D, 3,6-dichloro-o-anisic acid (dicamba), and 4-amino-3,5,6-trichloropicolinic acid (picloram) was inhibited in the presence of either chlorpropham or S-ethyl dipropylthiocarbamate (EPTC). Similarly, curvature tests using soybean (Glycine max (L.) Merr.) hypocotyl sections showed the curvature induced by the growth regulators to be almost completely eliminated by the presence of the carbamates.

The uptake and release of 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine) by green sunfish (Lepomis cyanellus Raf.) were measured during a 3-week exposure to either non-labeled or symmetrically ring-labeled 14C-simazine. Exposure was by feeding (3 and 10 mg/kg body wt) or bath (1 and 3 ppm). To determine the retention of simazine, treated fish remaining after exposure and sampling were placed in fresh water for 4 weeks. This water was changed weekly. Fish in the bath absorb simazine in amounts directly proportional to the concentration in the water: i.e., 0.95 and 2.29 ppm total residue after 3 weeks exposure to 1.0 and 3.0 ppm, respectively. Little or no simazine was found in feed-exposed fish 72 hr after feeding. Almost all of the residue was in the viscera. No simazine residue was detected in fish from the water bath exposure after they had been in fresh water 7 days.

The release of 3-amino-2,5-dichlorobenzoic acid (amiben), 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine), isopropyl m-chlorocarbanilate (chlorpropham), S-ethyl dipropylthiocarbamate (EPTC), and 3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea (linuron) from excised soybean (Glycine max (L) Merr., var. Chippewa) roots following uptake of the herbicides from solutions for 1 hr was studied. Rates of release of herbicides into water were rapid with at least 30% of that taken up being released during the first 30 min. Herbicide X time and herbicide X concentration interactions were highly significant. In most instances, slow release continued for 4 hr, which was the duration of the experiment. Use of herbicide or nutrient solutions as release solutions did not significantly change the amounts of herbicides released. It was concluded that herbicide molecules released after 1 hr uptake were those that had diffused out from free space rather than those released from uptake or adsorptive sites.

Scarification of freshly harvested redweed (Melochia corchorifolia L.) seed for 15 to 30 s in an electric scarifier equipped with 100- to 120-grit emery cloth resulted in the best germination. Scarified seed germinated best at 35 and 40C. At 10 and 45C there was no germination even after 7 days. Seven days after planting in silt loam soil there was 80 to 90% emergence of redweed from depths of 1 to 5 cm, whereas no emergence was observed from depths of 0, 8, or 10 cm.

Detached leaves and whole plants of quackgrass [Agropyron repens (L.) Beauv. # AGRRE] were used to study uptake and translocation of butyl esters of 14C-fluazifop {(±)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid}, with or without additional adjuvants. In the absence of adjuvants 3.2% of applied radioactivity entered detached quackgrass leaves by 6 h, and at the end of 24 h, 6.0% had penetrated. The presence of additives increased uptake by leaves significantly. In the presence of the nonionic surfactant Agral (nonyl phenol ethoxylate) at 0.2% (v/v) or the oil-additive Actipron (self-emulsifying adjuvant oil) at 2.0% (v/v), 17.2 and 12.9% of applied radioactivity, respectively, entered the leaves by 24 h. Evidence of dependence of phloem translocation of the radioactivity on source-sink relationships of the plant was obtained in the studies with whole plants. Translocation measured up to 7 days after treatment showed that radioactivity was concentrated in areas such as young developed leaves, young stems, and rhizome apices. Rhizomes appear to be major sinks for the accumulation of radioactivity and at 7 days 0.5% of applied radioactivity was found there. In wholeplant experiments the two adjuvants either individually or in mixture increased the uptake of 14C-fluazifop significantly. However, a corresponding increase in basipetal translocation was found only in one experiment. Much of the increased activity that had entered the leaves in the presence of adjuvants was found to have moved to areas distal to the treated zone or remained within the treated zones. In all experiments, applied 14C was not fully recovered. Evidence of significant volatility losses from treated surfaces was obtained and it is thought that this may be the main reason for the inability to recover all of the applied activity.

The development of early-maturing soybean [Glycine max (L.) Merr.] varieties has led to an increase in soybean production in canola (Brassica napus L.)-dominant crop rotations in western Canada. Herbicide-resistant (HR) volunteer B. napus can be difficult to manage in HR soybean using herbicides alone. In 2013 and 2014, four field experiments were conducted in Manitoba, Canada, to evaluate soybean row spacing, seeding density, nitrogen supply, and interrow tillage as candidate nonchemical weed management tools for an integrated program to manage volunteer B. napus in soybean. Among treatments and sites, volunteer B. napus produced about 830 seeds plant−1 and resulted in large seedbank inputs (averaging about 20,300 seeds m−2). Volunteer B. napus seedling recruitment differed among sites, and resulted in two distinct classes of sites based on average seedling densities of 39 and 89 plants m−2. Weed management tools were more effective at the sites with higher volunteer B. napus densities. At these sites, soybean yield was greater when using an increased soybean-seeding density (44% greater yield using a seeding density of 682,500 vs. 455,000 seeds ha−1) or interrow tillage (36% greater yield with vs. without using interrow tillage). Soybean row spacing (19 vs. 38 vs. 76 cm) did not affect soybean yield, unless the reduction in row spacing was combined with an increased seeding density (65% greater yield with narrow-row soybean seeded at 682,500 vs. wide-row soybean seeded at 455,000 seeds ha−1). At the sites with higher volunteer B. napus densities, seed production of canola volunteer B. napus was greater when nitrogen fertilizer was applied to simulate an environment with greater nitrogen supply (77% greater number of volunteer B. napus seeds produced with vs. without broadcast application of 23 kg N ha−1 urea). In northern climates, seeding soybean at increased densities using narrow-row spacing in fields with limited soil inorganic nitrogen and using interrow tillage in wide-row production systems are effective strategies that could augment chemical weed management in an integrated program for management of volunteer B. napus, and perhaps also other competitive early-season weeds.

Weeds pose a great problem to farmers worldwide, and controlling weeds demands a high input cost for herbicides and labor. Because of current environmental regulations, a limited number of herbicides are commercially available (with limited modes of action) to control weeds. Smoke water and the biologically active compounds isolated from smoke affect seed germination in a significant way. Smoke water (SW) and karrikinolide (KAR1, the germination stimulant isolated from smoke) have been tested extensively for their ability to promote seed germination in a vast array of plant species. In addition to KAR1, a germination inhibitor, trimethylbutenolide (TMB), was also isolated from plant-derived smoke. The effects of SW, KAR1, and TMB were tested on five major weed species of South Africa: fleabane, hairy wild lettuce, bugweed, spilanthes, and fameflower. Seeds of these weed species were subjected to 16/8 h light/dark conditions or to constant dark conditions at constant temperatures of 20, 25, 30 C and alternating 30/20 C. SW and KAR1 significantly increased germination, whereas TMB significantly inhibited germination of these weed species. Furthermore, TMB treatment reduced the amylase activity of the tested weed seeds compared with the water control. These results indicate the possibility of manipulating germination of certain weed seeds by SW, KAR1, and TMB. Thus, smoke and smoke-isolated compounds could potentially be used in new weed management strategies.

The most common strategy recommended for management of jointed goatgrass infestations is to rotate from winter wheat to a spring crop for several years. A field study was conducted at three locations in 1998 and 1999 to determine the effects of spring seeding date on the ability of jointed goatgrass to flower and produce viable seed in the presence or absence of spring wheat and to determine the effect of jointed goatgrass competition and crop seeding date on spring wheat grain yield. Spring wheat was seeded on four dates at each location in both hand-sown and natural jointed goatgrass infestations. Jointed goatgrass plants from hand-sown spikelets flowered and developed spikelets on all seeding dates except the last; viable seed was produced on the two earliest seeding dates. Jointed goatgrass plant densities from natural infestations were from 1 to 12 plants m−2, and spikelet production ranged from 0 to 480 spikelets m−2. Natural jointed goatgrass infestations produced spikelets containing viable seed on all seeding dates at one location in 1998, the driest location. Spring wheat yield was not affected by jointed goatgrass competition; however, jointed goatgrass spikelet production was reduced by spring wheat competition compared with that of monoculture jointed goatgrass. The last seeding date of spring wheat was associated with 51% less crop yield compared with the recommended seeding date. The decision to manage jointed goatgrass infestations with a spring crop rotation should consider delayed seeding dates to minimize viable spikelet production by spring-germinating jointed goatgrass; however, the cost of this decision may include grain yield reduction.

Distribution of 14C-glyphosate [N-(phosphonomethyl)glycine] in chemically treated and physically manipulated common milkweed [Asclepias syriaca (L.) ♯ ASCSY] was studied in greenhouse and growth chamber experiments. Pretreatment with glyphosate at 0.6 and 1.1 kg ae/ha 3 days prior to 14C-glyphosate application to leaves reduced the concentration of 14C recovered from shoots and leaves above the 14C-glyphosate-treated leaves but had no influence on the concentration of 14C in proximal root buds. Partial removal of the shoot and root prior to the application of 14C-glyphosate increased bud respiration and the concentration of 14C in the proximal root buds. Proximal root buds treated with 1 mM of 6-benzyl-aminopurine (BAP) for 6 days (3 days prior to application of 14C-glyphosate) contained seven times more 14C/mg than root buds of BAP-untreated plants, suggesting that dormant buds could be chemically stimulated to accumulate higher concentrations of glyphosate. BAP-treated buds were killed by foliar applications of glyphosate at 1.1 kg/ha, indicating that proximal root buds can be stimulated to acquire lethal concentrations of glyphosate.

Single-leaf CO2 assimilation rate under saturating light (CA) varies as a function of leaf nitrogen content per unit leaf area (NL). Measured CA for many crop species also declines with developmental stage. Because these relationships may have strong implications for crop–weed competition, a field experiment was conducted to quantify corn and velvetleaf CA as influenced by leaf NL and stage of development. Crop and weed CA were measured on the most recent fully expanded leaves of plants grown in four nitrogen (N) application treatments. Both corn and velvetleaf CA increased with increasing NL, up to about 1.5 g N m−2. Corn and velvetleaf NL values were rarely less than 0.75 g N m−2, indicating that both species may restrict leaf growth in order to maintain constant NL under conditions of limited soil N. Corn CA declined to half its maximum by physiological maturity, whereas velvetleaf CA only declined 18%. Although velvetleaf CA was considerably lower than that of corn, the difference decreased as the growing season progressed. Because corn leaf production is complete by anthesis and velvetleaf continues vegetative production throughout its life cycle, velvetleaf will produce relatively greater quantities of biomass late in the season, which may increase competition for light.

The preemergence herbicide N, N-dimethyl-2, 2-diphenylacetamide (diphenamid) alone and in combination with the contact herbicides 1,1′-dimethyl-4, 4′-bipyridinium salt (paraquat) and 3, 4-dichloropropionanilide (propanil) was studied over three years. Application at planting and crop emergence (delayed preemergence) were compared. Weed control and crop tolerance were equally effective at either stage in tomatoes. Delayed preemergence applications of contact materials alone were erratic as herbicides but were more effective in peppers than in tomatoes. At emergence, combinations were more effective. Selectivity of propanil lessened when the cotyledons of tomato expanded fully.

A relationship has been noted between environmental conditions, including soil characteristics, and the movement, persistence and activity of herbicides applied to the soil. Field studies have often given differing, and sometimes contradictory results, possibly because of different environments. Empirical studies cannot fully explain these differences.

Amitrole (3-amino-1,2,4-triazole) and 5-chlorobenzo-1,2,3-triazole were the only compounds tested that inhibited wheat root elongation and growth of carrot explants, produced chlorosis, and depressed catalase activity. Ten other heterocyclic compounds were more effective in inhibiting growth in wheat roots or carrot explants. Overall biological activity was reduced when substituents other than the amino group on the number three position were substituted on the triazole nucleus.

The WEEDSIM bioeconomic model was developed in Minnesota and was designed to support weed management decisions for both soil-applied and postemergence weed control programs in Zea mays and Glycine max. In this research, we adapted the WEEDSIM weed management model to Michigan by modifying the crop yield loss functions and herbicide efficacy ratings. We then validated the components of the model and determined whether WEEDSIM led to more profitable weed management than recommendations from SOYHERB or CORNHERB, computer decision aids based solely on herbicide efficacy and cost. The crop year significantly influenced the weed-free yield in Z. mays and G. max, but the weed—crop interference function did not change each year. Total weed seed increased in the untreated compared with the weed-free control over the 3-yr period. Weed seed did not increase significantly in WEEDSIM preemergence/postemergence (PRE/POST), WEEDSIM postemergence, or CORNHERB or SOYHERB treatments compared with the weed-free control, although annual grass seedling density at the time of postemergence herbicide application had increased by 1995 in the WEEDSIM postemergence treatment in G. max because of a 2,4-D amine application only in Z. mays in 1994. WEEDSIM PRE/POST and CORNHERB provided excellent weed control in all three years, and WEEDSIM PRE/POST resulted in gross margins over weed control costs equal to or greater than CORNHERB recommendations. In G. max, Chenopodium album and annual grass control was excellent in all three years for WEEDSIM PRE/POST, WEEDSIM postemergence, and SOYHERB treatments. The highest average gross margin for the 3-yr study was from mechanical weed control in 76-cm-wide rows of G. max ($806 ha−1) and from SOYHERB in 38- and 19-cm-wide rows of G. max ($776 and $808 ha−1, respectively). WEEDSIM recommendations controlled weeds and maintained crop yield in both Z. mays and G. max.

The methyl ester of diclofop {2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid} applied at 0.8 to 1.4 kg ai/ha and incorporated prior to seeding winter wheat (Triticum aestivum L.) controlled downy brome (Bromus tectorum L. ♯ BROTE) better than when applied preemergence at 1.7 kg/ha in 2 of 4 yr. The emulsifiable concentrate and a granular formulation of diclofop performed similarly. Controlling downy brome improved wheat yields 3 of 4 yr. However, preplant-incorporated applications of diclofop at 1.4 kg/ha reduced wheat yield 1 of 4 yr. Greenhouse data indicated that diclofop dissipated more rapidly in moist soil than in air-dry soil.

Field experiments determined the critical period for weed control (CPWC) in grafted and nongrafted watermelon [Citrullus lanatus (Thumb.) Matsum. & Nakai] grown in plasticulture. Transplant types included ‘Exclamation’ seedless watermelon as the nongrafted control as well as Exclamation grafted onto two interspecific hybrid squash (ISH) rootstocks, ‘Carnivor’ and ‘Kazako’. To simulate weed emergence throughout the season, establishment treatments (EST) consisted of two seedlings each of common purslane (Portulaca oleracea L.), large crabgrass [Digitaria sanguinalis (L.) Scop.], and yellow nutsedge (Cyperus esculentus L.) transplanted in a 15 by 15 cm square centered on watermelon plants at 0, 2, 3, 4, and 6 wk after watermelon transplanting (WATr) and remained until the final watermelon harvest at 11 WATr. To simulate weed control at different times in the season, removal treatments (REM) consisted of two seedlings of the same weed species transplanted in a 15 by 15 cm square centered on watermelon plants on the same day of watermelon transplanting and allowed to remain until 2, 3, 4, 6, and 11 WATr, at which time they were removed. Season-long weedy and weed-free controls were included for both EST and REM studies in both years. For all transplant types, aboveground biomass of weeds decreased as weed establishment was delayed and increased as weed removal was delayed. The predicted CPWC for nongrafted Exclamation and Carnivor required only a single weed removal between 2.3 and 2.5 WATr and 1.9 and 2.6 WATr, respectively, while predicted CPWC for Kazako rootstock occurred from 0.3 to 2.6 WATr. Our study results suggest that weed control for this mixed population of weeds would be similar between nongrafted Exclamation and Exclamation grafted onto Carnivor. But the observed CPWC of Exclamation grafted onto Kazako suggests that CPWC may vary with specific rootstock–scion combinations.

Cover crops enhance the biodiversity of cropping systems and can support a variety of useful ecosystem services, including weed suppression. In California orchards, cover crops are typically implemented as annual plants that can replace resident vegetation in orchard alleyways during the rainy winter season. Our research objective was to evaluate cover crop management factors that support a competitive, weed-suppressing cover crop in the unique orchard systems of central California. We conducted two experiments: an experiment evaluating cover crop management intensification in walnuts (Juglans regia L.) and an experiment evaluating multispecies cover crop mixes and planting date in almonds [Prunus dulcis (Mill.) D.A. Webb]. These experiments demonstrate that timely cover crop planting is important for producing an abundant cover crop, and a variety of cover crop management programs can produce weed-suppressing cover crops. However, cover crops do not result in weed-free orchards and should be considered within the context of integrated management programs. The apparent flexibility of orchard cover crop management provides an opportunity to promote other agroecosystem services, with vegetation management and weed suppression as complementary management goals.